The present invention relates to forming molded glass fiber reinforced polyester articles, particularly panel-shaped articles such as swimming pool walls and the like. Such articles typically have a smooth, plastic skin or film which defines the exterior shape of the article. Alternatively, a very smooth mold surface is provided against which the resin is cast. Glass fiber cloth saturated with resin is then layed against the film or smooth or intentionally textured mold wall and more resin is painted or rolled into place. Alternatively, a mixture of resin and chopped glass is sprayed onto the film. Sometimes, a combination of both processes are used.
Unfortunately, it is very difficult to prevent the formation of air bubbles between the polyester resin layer and the surface film or the mold surface. It is also difficult to achieve a complete bond, and delamination sometimes results.
There is also a significant environmental problem involved in these prior art techniques. The vapors of the solvent used to carry the polyester resin readily escape into the working environment when one is painting or spraying the resin in place. If at all possible, this condition should be avoided. Fumes tend to be particularly bad in spraying operations.
Further, even when you spray the resin onto this film, you usually have to use a roller to try to roll out air bubbles and insure a tight fit.
Another type of molding is known as bag forming. After resin is located in a female mold, a flat bladder is sucked down against the resin surface to squeeze the resin against the female mold. However, this method has been particularly unsuccessful in connection with larger articles, such as large panels of the type used in swimming pool walls, and with reinforced resins. There are simply too many air bubbles which are not eliminated through the use of this method. When air is removed from the mold, resin is also removed. Further, it is extremely difficult to keep reinforcing ribs which might be placed against the film from shifting around as the bladder is drawn up against the resin.
Yet another alternative is to provide matching male and female metal molds. The polyester resin and chopped glass are then injected into the mold cavity under a relatively high pressure, i.e. 20-30 psi. Unfortunately, the mold for such a process is extremely expensive. It becomes particularly costly when the molded article has to be provided with undercuts.